The use of calcined Mg–Al hydrotalcite as an efficient catalyst for the selective O-alkylation of catechol with dimethyl carbonate (DMC) to guaiacol in a continuous fixed bed flow reactor is described. A maximum guaiacol yield of 80% is obtained at 573 K under optimized conditions with a stable catalytic activity. A concerted mechanism involving acid–base pair sites in which a nucleophilic attack at the methyl carbon atom of DMC by the oxygen atom of the H-bonded phenolic compound or phenolate anion is proposed.